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| #1150016 (Received by flhurricane at: 4:59 AM 29.Aug.2023) TCDAT3 Hurricane Franklin Discussion Number 35 NWS National Hurricane Center Miami FL AL082023 500 AM EDT Tue Aug 29 2023 Near the time of the prior advisory, we received a GPM microwave pass at 0231 UTC, strongly suggesting the initial stages of an eyewall replacement cycle (ERC) were underway. This observation is also supported by the recent trends on infrared satellite imagery, which show the coldest cloud tops relative to Franklin`s warm eye becoming more focused towards outer concentric bands seen earlier on microwave imagery. Finally, a recently received 0635 UTC AMSR2 microwave pass confirms the ERC is ongoing, with the outer eyewall already starting to become dominant on the 89-GHz channel. All this data means is that the hurricane is likely past its peak intensity, but may be broadening its inner-core wind field as it undergoes this structural change. Subjective final T-number intensity estimates were 6.0/115 kt from both TAFB and SAB, with UW-CIMSS ADT also at T6.0/115 kt. However since the earlier aircraft data showed that Franklin was stronger than the satellite signature would suggest, the initial intensity is only being lowered to 120 kt for this advisory. Franklin is now beginning to lose longitude again, with the latest estimated motion at 015/8 kt. A further turn to the northeast is expected later today as the hurricane becomes caught in the flow between a subtropical ridge positioned to its southeast and an approaching mid-latitude trough ejecting out of Canada from the northwest. Ultimately, this trough is still forecast to capture Franklin, though the along-track spread remains high beyond the next 48 h. Once again the GFS and ECMWF are book-ending the track guidance this cycle, with the GFS the fastest and furthest north, and the ECMWF the slowest and furthest south, missing the trough connection. The ensemble guidance also continues to exhibit large spread between these scnerios after the next 48 h. The NHC track forecast continues to favor a solution closest to the the consensus aids TVCA and HCCA, which trended a bit slower this cycle. On the forecast track, Franklin should bypass Bermuda well to the northwest on Wednesday, but tropical-storm-force winds associated with Franklin will come much closer to the island due to the hurricane`s large and expanding wind field. With the ongoing eyewall replacement cycle, Franklin is likely past its peak intensity. It is forecast to continue weakening, especially as the hurricane also begins to move over cooler waters. In addition, shear out of the northwest increases markedly in both the GFS and ECMWF forecasts after 48 hours, which should hasten the weakening process. The latest NHC intensity forecast is again a bit lower than the previous cycle, but remains somewhat higher than the consensus aids which show a slightly faster rate of weakening. There are still timing differences in the guidance regarding exactly when Franklin will become extratropical. The day 4 extratropical transition time frame in the NHC official forecast is a compromise between the faster GFS and slower ECMWF solutions. KEY MESSAGES: 1. Tropical storm conditions are possible on Bermuda beginning Wednesday morning, when Franklin is forecast to make its closest approach to the island. 2. Life-threatening surf and rip currents are occurring along the coast of the southeast United States. These conditions are expected to spread northward along the remainder of the U.S. east coast, Atlantic Canada, and Bermuda later today into Wednesday. FORECAST POSITIONS AND MAX WINDS INIT 29/0900Z 30.2N 70.8W 120 KT 140 MPH 12H 29/1800Z 31.3N 70.3W 110 KT 125 MPH 24H 30/0600Z 33.0N 68.8W 100 KT 115 MPH 36H 30/1800Z 34.8N 66.3W 95 KT 110 MPH 48H 31/0600Z 36.7N 62.8W 90 KT 105 MPH 60H 31/1800Z 38.6N 58.5W 80 KT 90 MPH 72H 01/0600Z 41.4N 53.1W 75 KT 85 MPH 96H 02/0600Z 48.2N 41.1W 65 KT 75 MPH...POST-TROP/EXTRATROP 120H 03/0600Z 59.1N 27.5W 50 KT 60 MPH...POST-TROP/EXTRATROP $$ Forecaster Papin |
